1. Field of the Invention
This invention relates generally to the field of synthetic fuel (synfuel) production. Specifically, the invention relates to a method of maximizing hydrogen and carbon utilization in synfuel production using carbonaceous material as primary feedstocks.
2. Background of the Invention
There are many processes known in the art for converting hydrocarbon sources such as natural gas, coal, coke, bio-mass, etc., into more valuable hydrocarbon products. A typical conversion process involves first converting the hydrocarbon source into synthesis gas or syngas, which is a mixture of primarily carbon monoxide and hydrogen. If the hydrocarbon source is natural gas, NG, a catalytic reforming reaction is utilized to make synthesis gas (partial oxidation processes are also used with NG). If the hydrocarbon source is residual oil or a solid feed, partial oxidation or gasification may be used. However obtained, the synthesis gas produced may subsequently be utilized as a feedstock from which to produce a wide range of chemical products. Such chemical products include combustible liquid fuels, methanol, ammonia, acetic acid, dimethyl ether, oxo alcohols, isocyanates, and others.
Remote natural gas assets can be converted into conventional transportation fuels, chemical feedstocks, and lubricants via an initial production of synthesis gas. The Fischer-Tropsch process is the conventional route for the conversion of synthesis gas into transportation fuels and lubricants. Alternatively, synthesis gas produced from natural gas may be used to synthesize methanol. The methanol may subsequently be utilized to produce a wide variety of chemicals.
In particular, a Fischer-Tropsch synthesis reaction may be used to synthesize higher molecular weight hydrocarbon products from synthesis gas. In Fischer-Tropsch synthesis reactions, synthesis gas is converted to hydrocarbons by contact with a Fischer-Tropsch catalyst under reactive conditions. The products from a Fischer-Tropsch process may range from C1 to C200+ with a majority in the C5-C100+ range. The Fischer-Tropsch synthesis reaction can be conducted in a variety of reactor types which include but are not limited to, fixed bed reactors containing one or more catalyst beds, slurry reactors, fluidized bed reactors, or a combination of different reactor types.
In traditional Fischer-Tropsch processes, high purity hydrogen may be extracted for downstream conversion or upgrading of crude liquid Fischer-Tropsch hydrocarbons into desirable saleable products. The liquid hydrocarbon conversion process or product upgrading as it is more commonly known, may comprise a series of processes, such as separations, hydrogenation (saturation) of the olefinic and oxygenated components formed in the Fischer-Tropsch reactor and hydro-cracking, isomerization, and/or hydro-isomerization processes to convert long chain usually linear hydrocarbons into shorter and partially-branched chain hydrocarbons to yield mainly liquid hydrocarbons with molecules of carbon and hydrogen in the range defined as naphtha, diesel fuel and jet fuel. Some products may also be used as base oils or lubricants. The processes to extract high purity hydrogen from synthesis gas may generate off streams “lean” in hydrogen compared to the hydrogen-rich stream desired for product upgrading. These “lean” hydrogen streams are conventionally inefficiently utilized as fuel for the production plant.
Consequently, there is a need for improved utilization of hydrogen in synthesis gas production plants.